I purchased a Montblanc 149 for $75.00.
But the most expensive pen was the Bic I used to sign the marriage license.
Ohto Tasche. I think it cost me about £10 Works great, perfect for daily carry, and I've had lots of compliments about it.
I think the most I ever paid for a pen was around £35-£40 for a ballpoint about 20 years ago. It failed quite dramatically one day, wrecking a shirt in the process. I've bought cheap pens ever since. No regrets.
I purchased a new Waterman Perception fountain pen some 5 years ago for $80.
It is a beautiful pen but definitely not intended to be used for extended writing sessions.
I mostly prefer my Pilot Metropolitan and Lamy Safari fountain pen over the Perception fountain pen.